'\" te
.\"  Copyright (c) 2002, Sun Microsystems, Inc. All Rights Reserved
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
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.TH KS_SNAPSHOT 9E "Sep 7, 2015"
.SH NAME
ks_snapshot \- take a snapshot of kstat data
.SH SYNOPSIS
.nf
#include <sys/types.h>
#include <sys/kstat.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>



\fBint prefix\fR\fB_ks_snapshot\fR(\fBkstat_t *\fR\fIksp\fR, \fBvoid *\fR\fIbuf\fR, \fBint\fR \fIrw\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI).
.SH PARAMETERS
.ne 2
.na
\fB\fIksp\fR \fR
.ad
.RS 8n
Pointer to a \fBkstat\fR(9S) structure.
.RE

.sp
.ne 2
.na
\fB\fIbuf\fR \fR
.ad
.RS 8n
Pointer to a buffer to copy the snapshot into.
.RE

.sp
.ne 2
.na
\fB\fIrw\fR \fR
.ad
.RS 8n
Read/Write flag. Possible values are:
.sp
.ne 2
.na
\fB\fBKSTAT_READ\fR\fR
.ad
.RS 15n
Copy driver statistics from the driver to the buffer.
.RE

.sp
.ne 2
.na
\fB\fBKSTAT_WRITE\fR\fR
.ad
.RS 15n
Copy statistics from the buffer to the driver.
.RE

.RE

.SH DESCRIPTION
The \fBkstat\fR mechanism allows for an optional \fBks_snapshot()\fR function
to copy \fBkstat\fR data. This is the routine that is called to marshall the
\fBkstat\fR data to be copied to user-land. A driver can opt to use a custom
snapshot routine rather than the default snapshot routine; to take advantage of
this feature, set the \fBks_snapshot\fR field before calling
\fBkstat_install\fR(9F).
.sp
.LP
The \fBks_snapshot()\fR function must have the following structure:
.sp
.in +2
.nf
static int
xx_kstat_snapshot(kstat_t *ksp, void *buf, int rw)
{
     if (rw == KSTAT_WRITE) {
/* set the native stats to the values in buf */
/* return EACCES if you don't support this */
     } else {
/* copy the kstat-specific data into buf */
     }
     return (0);
}
.fi
.in -2
.sp

.sp
.LP
In general, the \fBks_snapshot()\fR routine might need to refer to
provider-private data; for example, it might need a pointer to the provider's
raw statistics. The \fBks_private\fR field is available for this purpose. Its
use is entirely at the provider's discretion.
.sp
.LP
No \fBkstat\fR locking should be done inside the \fBks_snapshot()\fR routine. The
caller will already be holding the \fBkstat\fR's \fBks_lock\fR (to ensure
consistent data) and will prevent the \fBkstat\fR from being removed.
.RS +4
.TP
1.
\fBks_snaptime\fR must be set (via \fBgethrtime\fR(9F)) to timestamp the
data.
.RE
.RS +4
.TP
2.
Data gets copied from the \fBkstat\fR to the buffer on \fBKSTAT_READ\fR, and
from the buffer to the \fBkstat\fR on \fBKSTAT_WRITE\fR.
.RE
.SH RETURN VALUES
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 10n
Success
.RE

.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 10n
If \fBKSTAT_WRITE\fR is not allowed
.RE

.sp
.ne 2
.na
\fB\fBEIO\fR\fR
.ad
.RS 10n
For any other error
.RE

.SH CONTEXT
This function is called from user context only.
.SH EXAMPLES
\fBExample 1 \fRNamed \fBkstat\fRs with Long Strings (\fBKSTAT_DATA_STRING\fR)
.sp
.in +2
.nf
static int
xxx_kstat_snapshot(kstat_t *ksp, void *buf, int rw)
{
    if (rw == KSTAT_WRITE) {
         return (EACCES);
    } else {
         kstat_named_t *knp = buf;
         char *end = knp + ksp->ks_ndata;
         uint_t i;

         bcopy(ksp->ks_data, buf,
                 sizeof (kstat_named_t) * ksp->ks_ndata);
/*
 * Now copy the strings to the end of the buffer, and
 * update the pointers appropriately.
 */
         for (i = 0; i < ksp->ks_ndata; i++, knp++)
                 if (knp->data_type == KSTAT_DATA_STRING &&
                     KSTAT_NAMED_STR_PTR(knp) != NULL) {
                         bcopy(KSTAT_NAMED_STR_PTR(knp), end,
                                 KSTAT_NAMED_STR_BUFLEN(knp));
                         KSTAT_NAMED_STR_PTR(knp) = end;
                         end += KSTAT_NAMED_STR_BUFLEN(knp);
                 }
    }
    return (0);
}
.fi
.in -2
.sp

.SH SEE ALSO
.BR ks_update (9E),
.BR kstat_create (9F),
.BR kstat_install (9F),
.BR kstat (9S)
.sp
.LP
\fIWriting Device Drivers\fR
